This invention relates to devices and method for heating prefrozen or refrigerated prepared meals by fast, microwave techniques. The invention is useful particularly when feeding large numbers of people as in institutional cafeterias, hospitals, fast food establishments, etc. The invention is also suited for use when feeding a limited number of people with special foods such as persons having particular dietary requirements as might be found in a nursing home.
Among the difficulties which have been encountered in the preparation and serving of complete meals by microwave heating has been that because the individual food components generally require different quantities of microwave energy exposure, it is difficult to control the precise exposure of all of the meal components at the same time and in the same oven. Recent years have seen important improvements in the development of differential heating containers receptive to a number of individual food components and which employ shielding means to control the amount of radiation to which each of the individual food components is exposed in the microwave oven. For example, U.S. Pat. No. 3,547,661 describes an enclosure for a multi-component meal in which the enclosure is opaque to the microwave radiation except for radiation-transparent windows formed in the enclosure to expose the various foods to different degrees of microwave energy. Although the techniques disclosed in that patent are believed to have solved the primary difficulties previously encountered (to selectively control the heating of the individual food components), other problems have surfaced in this art. For example, it may sometimes occur that when the meal is heated and served in a multi-compartmented tray, the ridges which separate and define the individual tray compartments may have become spattered or coated with food such as sauce or gravy which results in a somewhat less than palatable appearance of the tray when the food is served. Additionally, there may be some instances in which some of the food components will tend to give off water vapor during the heating process which may condense in droplets on some of the surfaces of the tray which are exposed when served. This, too, detracts from the appearance of the meal.
During the simultaneous heating of the food components, it is desirable that each of the individual food components be isolated from each other to preclude migration of food odors and water vapor between the food compartments. It therefore is desirable to employ some form of sealing arrangement to isolate the food compartments from each other. It is desirable that the seal be effective for its purpose yet also be easily broken so that the tray and cover may be separated easily without requiring difficult or awkward manipulations which could result in rough handling of the container. Such rough handling could cause some of the food components to smear the internal surfaces of the tray with resultant messy appearance of the tray when the cover is removed. If the manipulations required to uncover the tray are excessively awkward, that could even result in the contents of the tray being accidentally spilled. For example, U.S. Pat. No. 3,835,281 to Mannix discloses a differential heating container in which the lid and cover are sealed to each other about their peripheral rims and also employ an interlocking arrangement between the lid and cover ridges which require relative rotation of the tray and cover in order to separate them. In order to remove the cover from the tray, the peripheral rim seal somehow must be broken and then the tray and cover must be rotated relative to each other. Such manipulation is considered undesirable.
Also among the problems which have presented themselves is that after the meal has been heated in the microwave oven, sauces, gravies or toppings often tend to flow to the bottom of the food compartments when it would be preferable for these food components to be on top of their associated food at the time that the meal is served. In addition, some foods tend to have a somewhat dried-out appearance on their upper surface after heating when it would be preferred that they appear moist.
It is among the general objects of the invention to provide both a device and technique which overcomes these difficulties.